Engine systems may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system (intake passage), a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions and improve fuel economy. An EGR system may include various sensors to measure and/or control the EGR. As one example, the EGR system may include an intake gas constituent sensor, such as an oxygen sensor, which may be employed during non-EGR conditions to determine the oxygen content of fresh intake air. During EGR conditions, the sensor may be used to infer EGR based on a change in oxygen concentration due to addition of EGR as a diluent. One example of such an intake oxygen sensor is shown by Matsubara et al. in U.S. Pat. No. 6,742,379. The EGR system may additionally or optionally include an exhaust gas oxygen sensor coupled to the exhaust manifold for estimating a combustion air-fuel ratio.
As such, due to the location of the oxygen sensor downstream of a charge air cooler in the high pressure air induction system, the sensor may be sensitive to the presence of fuel vapor and other reductants and oxidants such as oil mist. For example, during boosted engine operation, purge air and/or blow-by gases may be received at a compressor inlet location. Hydrocarbons ingested from purge air, the positive crankcase ventilation (PCV), and/or rich EGR can consume oxygen on the sensor catalytic surface and reduce the oxygen concentration detected by the sensor. In some cases, the reductants may also react with the sensing element of the oxygen sensor. The reduction in oxygen at the sensor may be incorrectly interpreted as a diluent when using the change in oxygen to estimate EGR. Thus, the sensor measurements may be confounded by the various sensitivities, the accuracy of the sensor may be reduced, and measurement and/or control of EGR may be degraded.
Hydrocarbons in the PCV flow may result from increased fuel in engine oil in a crankcase of the engine. For example, fuel may accumulate in the engine oil during engine cold start and warm-up conditions. The accumulated fuel may then be released as hydrocarbons while the engine is warming up and when the engine oil reaches a steady-state operating temperature. Hydrocarbons may affect various engine parameters and controls including fuel control and monitoring, engine oil viscosity, and the intake oxygen sensor output. Excessive fuel in the oil may decrease engine durability.
In one example, the issues described above may be addressed by a method for an engine comprising: adjusting engine operation based on a fuel concentration in engine oil, the fuel concentration based on an output of an intake oxygen sensor when purge and EGR flow are disabled, engine oil temperature, and fuel composition. A fuel evaporation from the engine oil may also be determined based on the estimated fuel concentration in engine oil. The fuel concentration in engine oil and the fuel evaporation rate may provide information as to the concentration of hydrocarbons in both the engine oil and the intake air when the engine is boosted. As a result, an engine controller may adjust engine operation based on the fuel concentration in engine oil and/or the fuel evaporation rate. In one example, the controller may correct an output of the intake oxygen sensor for EGR flow estimation based on the fuel concentration in the engine oil. Subsequently, the controller may adjust an EGR valve based on the estimated EGR flow. In another example, the controller may adjust fuel injection to the engine based on the fuel evaporation rate. For example, as the fuel evaporation rate increases, the controller may decrease an amount of fuel injection. In yet another example, the controller may use the fuel evaporation rate to predict subsequent intake oxygen readings from the intake oxygen sensor. If the predicted intake oxygen reading differs from an actual output of the intake oxygen sensor, the fuel evaporation rate estimation may be degraded and accurate compensation of the output of the intake oxygen sensor for EGR control may not be possible. As a result, the controller may indicate degradation of the estimation method and trigger a method to disable EGR flow until the hydrocarbon effect is reduced. In this way, adjusting engine operation based on the fuel concentration in engine oil and/or the fuel evaporation rate may increase the accuracy of engine control by providing a way to predict an amount of hydrocarbons in the intake airflow and subsequently adjust engine fueling and/or EGR flow based on the hydrocarbons in the airflow and engine oil. As a result, engine longevity may be increased and EGR flow may be delivered at a requested level.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.